Menstrual cycle is the reproductive cycle in all primates and begins at puberty. The process of setting in of Menstrual cycle in human females at puberty is called menarche.
What is this menstrual cycle?- Let us analyze this.
The cycle of events starting from one menstruation till the next one is called the menstrual cycle.
Under normal conditions, in human females, the average length of the menstruation cycle is 28 to 29 days. However, it is extremely variable. Any factor that can alter the hormonal balance in the body can alter this menstrual cycle. It is well known that heavy exercise, illness, physical or emotional stress, poor diet, forced starvation or self-imposed anorexia, and many other conditions can lengthen the menstrual cycle time, or make the menstrual cycle stop indefinitely.
Menstrual cycle consists of 3 phases:
i)Menstrual phase
ii)Follicular phase
iii) Luteal phase
Menstrual phase
The cycle starts with the menstrual flow (3 to 5 days), caused due to the breakdown of the endometrium* of the uterus. Blood vessels in liquid state are discharged, but this occurs only when the ovum is not fertilised.
Note: * Human uterus is also called womb, and it is pear shaped.It is connected to the pelvic walls by ligaments.The uterine wall consists of:
○ External perimetrium-it is the external wall & it is thin membranous in nature.
○ Middle myometrium- it is the middle thick layer, consisting of smooth muscles.
○ Internal endometrium- it is the inner glandular layer. It lines the uterine cavity.
The endometrium undergoes changes during the menstrual cycle.
Follicular phase
It is followed by the follicular phase. In this phase, the primary follicles mature into the Graffian follicles. This causes the regeneration of the endometrium.
These changes are brought about by ovarian and pituitary hormones.
In this phase, the release of gonadotropins from pituitary gland (LH and FSH) increases. This causes follicular growth in the ovaries and the growing follicles produce estrogen from ovaries.
Note: An estrogen test measures the level of the most important estrogen hormones (estradiol, estriol, and estrone) in a blood or urine sample. Estradiol is the most commonly measured type of estrogen for non-pregnant women.
During the middle of the menstrual cycle, one ovum is released & it is called ovulation. If the ovum gets fertilized by the sperm then it results in the formation of Zygote & complete development of this zygote results in the formation of new human being.
The Luteinizing hormone (LH) and Follicle Stimulating hormone (FSH) are at their peak in the middle of the cycle (14th day), and cause the rupture of the Graffian follicles (matured follicle) to release ovum. This phase is called the ovulatory phase.
Luteal Phase
The remains of the Graffian follicles get converted into the corpus luteum, which secretes progesterone for the maintenance of the endometrium layer of uterus.
In the absence of fertilisation, the corpus luteum degenerates, thereby causing the disintegration of the endometrium and the start of a new cycle.
In human females, the menstrual cycle ceases to operate at the age of 50 years. This phase is known as the menopause.
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